Work through each stage in order. The next step unlocks only after you confirm the current one is complete.
Safe isolation is the process of disconnecting a circuit from its supply and proving it dead before any work begins. Failure to follow the correct sequence is one of the most common causes of electrical fatalities in the UK. The procedure below follows the HSE GS38 guidance and the requirements of the Electricity at Work Regulations 1989.
The sequence matters. Proving the test instrument works before and after testing the circuit (steps 4 and 7) is not optional — a faulty test instrument will give a false dead reading on a live circuit. This two-stage instrument check is what separates the procedure from simply pointing a meter at the terminals.
For three-phase supplies, all three phases and the neutral must be proved dead. A circuit that reads dead on one phase may still be live on another — never assume.